Olefins are used in various reactions to produce important chemical compounds. Accordingly, demand for olefins is ever increasing and therefore new processes or increased efficiencies in existing processes are required. One of the main processes used in preparing light olefins is naphtha steam cracking. It is known that the efficiency of steam cracking depends on the specific composition of the naphtha feed. Specifically it has been demonstrated that converting naphthenes to acyclic paraffins, e.g. n-paraffins significantly improves olefin yield from the steam cracker. There is, therefore, a need for an improved ring opening catalyst.
Improved ring opening catalysts are also necessary because of increasing demand for environmentally friendly products and clean burning high performance fuels. In this case naphthene rings are opened to give acyclic paraffins which in turn can be isomerized. These isomerized paraffins have improved characteristics than the corresponding naphthenes.
An increased amount of paraffins is also required in providing reformulated gasoline. Reformulated gasoline differs from the traditional product in having a lower vapor pressure, lower final boiling point, increased content of oxygenates, and lower content of olefins, benzene and aromatics.
Reduction in gasoline benzene content often has been addressed by changing the cut point between light and heavy naphtha, directing more of the potential benzene formers to isomerization instead of to reforming. No benzene is formed in isomerization, wherein benzene is converted to C6 naphthenes and C6 naphthenes are isomerized toward an equilibrium mixture of cyclohexane and methylcyclopentane or converted to paraffins through ring opening. It is believed that such C6 cyclics are preferentially adsorbed on catalyst sites relative to paraffins, and the cyclics thus have a significant effect on catalyst activity for isomerization of paraffins. Refiners thus face the problem of maintaining the performance of light-naphtha isomerization units which process an increased concentration of feedstock cyclics.
Catalysts which are useful for ring opening are known and include a high chloride platinum component dispersed on a refractory inorganic oxide which is described in U.S. Pat. No. 5,463,155. U.S. Pat. No. 5,811,624 describes a catalyst for the selective opening of 5 and 6 membered rings which consists of a transition metal catalyst selected from the group consisting of carbides, nitrides, oxycarbides, oxynitrides, and oxycarbonitrides. The transition metal is selected from the group consisting of metals from Group IVA, VA, VIA of the Periodic Table of the Elements. U.S. Pat. No. 6,235,962 B1 discloses a catalyst for ring opening which comprises a carrier consisting of alumina, a metal modifier selected from the group consisting of scandium, yttrium and lanthanum, and at least one catalytically active metal selected from the group consisting of platinum, palladium, rhodium, rhenium, iridium, ruthenium, and cobalt. U.S. Pat. No. 5,382,730 discloses a process for ring opening and isomerization of hydrocarbons where the catalyst comprises an aluminosilicate zeolite such as Zeolite Y or Zeolite Beta and a hydrogenation component. U.S. Pat. No. 5,345,026 discloses a process for conversion of cyclic hydrocarbons to non-cyclic paraffin hydrocarbons where the catalyst comprises a hydrogenation-dehydrogenation component and an acidic solid component comprising a group IVB metal oxide modified with an oxyanion of a group VIB metal. U.S. Pat. No. 3,617,511 discloses a catalyst for conversion of cyclic hydrocarbons to paraffins where the catalyst comprises rhodium or ruthenium on a halogen promoted refractory oxide. U.S. Pat. No. 6,241,876 discloses a ring opening catalyst which comprises a large pore crystalline molecular sieve component with a faujasite structure and an alpha acidity of less than one and a Group VIII noble metal. U.S. Publication No. 2002/43481 A1 discloses a catalyst for naphthalene ring opening which comprises at least one Group VIII metal selected from iridium, platinum, rhodium and ruthenium on a refractory inorganic oxide substrate containing at least one of an alkali metal and alkaline earth metal. Finally U.S. Publication No. 2002/40175 A1 discloses a naphthene ring opening catalyst comprising a Group VIII metal selected from iridium, platinum, palladium, rhodium, ruthenium and combinations thereof. With the metal being supported on the substrate comprising at least one of a Group IB, IIB, and IVA metal.
Applicants have developed an improved catalyst which takes cyclic paraffins such as methylcyclohexane and converts them to normal or branched paraffins of substantially the same carbon number. The catalyst comprises a Group VIII (IUPAC 8-10) metal component, a molecular sieve, a modifier component and a refractory inorganic oxide. The molecular sieves include those having 8, 10 or 12 ring pores and which promote minimal or no cracking, while preferred Group VIII metals include platinum and palladium and modifiers include niobium and titanium.